Wearing protective face masks has become standard procedure for many health care and other related activities. The use of a face mask is important, for example, to lab technicians while conducting tests, to nurses in the care of patients, to physicians during surgery and other medical treatment, and to dentists working in a patient's mouth.
The rapid increase of infectious diseases, particularly AIDS, has made the use of such protective equipment increasingly important. The Center for Disease Control in Atlanta, Ga., has found that the AIDS virus (HIV) can be passed by contact with body fluids. Contact of AIDS contaminated body fluids with another person's source of body fluids, e.g., eyes, nose, mouth, etc., can pass the disease.
During the past several years, health care personnel have become more aware of the potential hazards associated with airborne pathogens, such as the hepatitis B virus and infectious tuberculosis (TB) associated with many HIV patients. It has been found that aerosols having airborne liquid and solid particles are generated not only by the exhalation of infected patients, but also by certain procedural manipulations and processes that impart energy to microbial suspensions. Also, many viral hemorrhagic fevers such as yellow fever, rift valley fever and perhaps rocky mountain spotted fever, rabies and smallpox can be transmitted through aerosols. A considerable number of studies have been made which are now beginning to identify the transmission of viruses through "non-accident" situations. Accordingly, there is an increased interest in using face masks or respirators which form a complete seal around the periphery of the mask and at the same time are easy to put on and comfortable to wear. Many face masks which are presently available allow the passage of fluids and/or aerosols between the periphery of the mask and the wearer's face.
The Department of Health and Human Services through the Centers for Disease Control and Prevention are currently preparing "Guidelines For Preventing The Transmission Of Tuberculosis In Health Care Facilities, Second Addition". One of the items which will be emphasized in the new guidelines is personal respiratory protection. The response to the draft guidelines published by the Department of Health and Human Services demonstrates the increased interest and importance of reducing the risk of tuberculosis transmission within health care facilities. The use of personal respiratory protective equipment in areas where there is a risk of exposure to mycobacterium tuberculosis such as tuberculosis isolation rooms where personnel with infectious tuberculosis are isolated is one of the important features of the new guidelines intended to reduce the risk to health care personnel.
The following comments are taken from the draft guidelines as published in the Federal Register, Volume 58, No. 195, Tuesday, Oct. 12, 1993, pages 52843-52845.
"Personal respiratory protection should be used by persons entering rooms where patients with known or suspected infectious TB are being isolated, during cough-inducing or aerosol-generating procedures on patients with known or suspected infectious TB, and in other settings where administrative and engineering controls are not likely to protect persons from inhaling infectious airborne droplet nuclei." Page 52843.
"Face-seal leakage. Face-seal leakage comprises the ability of particulate respirators to protect the worker from airborne material (148--ANSI1980, 149--Hyatt1963, 150--ANSI1961). A proper seal between a respirator's sealing surface and a wearer's face is essential for effective and reliable performance of any negative-pressure respirator. It is less critical, but still important, for a positive-pressure respirator. Face-seal leakage can result from factors such as incorrect facepiece size or shape, incorrect or defective facepiece sealing-lip, beard growth on a wearer, perspiration or facial oils that can result in facepiece slippage, failure to use all the headstraps, incorrect positioning of a facepiece on a wearer's face, incorrect headstrap tension or position, improper mask maintenance, and mask damage.
The mechanism of action of negative-pressure (non-powered) particulate respirators is based on the same principle. During each inhalation by a wearer, a negative pressure (relative to the workplace air) is created inside the facepiece of this type of respirator. Due to this negative pressure, air containing contaminants can take a path of least resistance into the respirator--through leaks at the face-seal interface--thus avoiding the higher-resistance filter material. Currently available, cup-shaped, disposable particulate respirators have 0% to 10% (148--ANSI1980) to 20% (151--NIOSH1987, 152--DCCIR1987) face-seal leakage. This leakage through the face seal results from limitations in the design, construction, number of sizes available of these masks, and the variability of the human face. The face-seal leakage is assumed to be even higher if the respirators are not properly fitted to the wearer's face, tested for an adequate fit by a qualified individual, and then checked for fit by the wearer every time these masks are dionned. Face-seal leakage may be reduced to less than 10% with improvements in design and more available sizes, combined with appropriate fit testing and fit checking." Page 52844.
"Fit Checking. A fit check is a maneuver that a HCW performs before each use of the respiratory protective device to check the fit. The fit check can be performed according to the manufacturer's facepiece fitting instructions or using a negative pressure test or a positive pressure test (Table S4-3).
Some currently available cup-shaped disposable negative-pressure particulate respirators with DM, DFM, or HEPA filters cannot be reliably fit checked by wearers (152--DCCIR1987), because it is difficult to occlude the entire surface of the filter. Strategies for overcoming these limitations are under development by respirator manufacturers but have not been evaluated." Page 52845.